Process for the aftertreatment of betaines and amphoteric surfactants

ABSTRACT

Process for the aftertreatment of betaine and amphoteric surfactants comprising adjusting the pH to the range of from 11 to 14 by addition of an alkali metal hydroxide, followed by a thermal aftertreatment if the surfactant contains dichloroacetic acid residues.

This application is a 371 of PCT/EP94/00621 filed Mar. 3, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the aftertreatment of betainesand amphoteric surfactants in which the surfactants are alkalized andsubjected to a thermal aftertreatment.

2. Statement of Related Art

Betaines and amphoteric surfactants show high compatibility with theskin and exhibit excellent cleaning properties. Accordingly, they areparticularly suitable for the production of a number of surface-activeproducts. In the most simple case, they are produced from tertiaryamines which are reacted with sodium chloroacetate to form alkylbetaines. The reaction of fatty acid amidoamines or imidazolines withsodium chloroacetate leads to the formation of amphoteric surfactants ofthe glycinate type. If acrylates are used as the alkylating agent,aminopropionates are formed. Compounds of the type mentioned aredescribed in a number of synoptic articles of which it is only intendedhere to cite Parf. Cosm. Arom. 70, 67 (1986), HAPPI, 70, (November 1986)and Soap Cosm. Chem. Spec. 46, (April 1990).

A particular concern in the production of betaines and amphotericsurfactants is to provide pure and hence dermatologically andtoxicologically safe products. For example, traces of chloroacetic acidand, more particularly dichloroacetic acid, in the surfactants areundesirable. Preservatives which are intended to protect the betainesand amphoteric surfactants against microbial contamination are alsofrequently undesirable, so that there is a further need for productswhich are stabilized against microbial contamination even without theaddition of auxiliaries. Finally, a third problem addressed by thepresent invention was to provide light-colored products.

A number of publications offering partial solutions to the cumulatedproblem are known from the prior art.

For example, it is proposed in DE-A1 39 39 264 (Henkel) to reduce thecontent of chloroacetic acid in amphoteric surfactants by subsequenttreatment of the aqueous solutions with ammonia, amino acids oroligopeptides. DE-OS 29 26 479 (Th. Goldschmidt) describes a process inwhich the quaternization is carried out at a pH value of 7.5 to 10.5 andthe residual content of free alkylating agent is thus reduced. Theteaching of DE-A 20 63 424 (Rewo), which describes pH adjustment for thealkylation of imidazolines, points in the same direction. However, theseprocesses do not have any influence on the content of dichloroaceticacid.

Sodium hypochlorite and, more particularly, hydrogen peroxide are usedto bleach surface-active compounds. Bleaching is generally carried outin a neutral or acidic medium because H₂ O₂ quickly decomposes underalkaline conditions. However, the acidic peroxide bleaching of betainesand amphoteric surfactants often produces only a temporary lightening ofcolor, the color darkening again after storage.

In addition, a process for the preservative-free stabilization ofspecial nonionic surfactants, so called alkyl polyglucosides, in whichthe aqueous solutions are adjusted to a pH value of at least 7, is knownfrom the literature (DE-A1 40 35 722, Henkel). However, in view of thedifferences in structure between the nonionic alkyl polyglucosides andthe betaines or amphoteric surfactants, which in addition also contain ahydrolyzable amide bond, application of the process to betaines andamphoteric surfactants appears to offer little promise.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the aftertreatment ofbetaines and amphoteric surfactants, in which the surfactants areadjusted to a pH value of 11 to 14 and preferably 12 to 13.5 by additionof alkali metal hydroxides and are subjected to a thermalaftertreatment, optionally under elevated pressure.

It has surprisingly been found that the thermal aftertreatment ofbetaine surfactants in a highly alkaline medium leads to a rapid andsubstantially quantitative reduction in the content of dichloroaceticacid. This was all the more surprising insofar as even betainescontaining an amide bond proved to be extremely resistant to hydrolysisunder these highly alkaline conditions and no significant change in theacid or amine value could be observed, even in the event of prolongedstorage. The invention includes the observation that the alkalized andaftertreated products are excellently stabilized against microbialcontamination so that there is no longer any need for additionalpreservation. Finally, it was surprisingly found that the highlyalkalized products obtained by the process according to the inventionare readily accessible to peroxide bleaching so that, unexpectedly,light-colored products can be obtained.

Betaines and amphoteric surfactants

Basically, the process according to the invention may be applied to anybetaines and amphoteric surfactants. Although the advantage of removingdichloroacetic acid does not of course apply to those types that are notproduced by alkalization with sodium chloroacetate, for exampleaminopropionates or sulfobetaines, the thermal aftertreatment of thehighly alkalized products stabilizes the surfactants against microbialcontamination even in these cases and makes the surfactants moreaccessible to peroxide bleaching.

However, the process according to the invention may be applied withadvantage to betaines of the alkyl betaine type which correspond toformula (I): ##STR1## in which R¹ is an alkyl and/or alkenyl radicalcontaining 6 to 22 carbon atoms and R² and R³ independently of oneanother represent an alkyl and/or hydroxyalkyl radical containing 1 to 4carbon atoms.

Typical examples are reaction products of tertiary amines, moreparticularly dimethyl alkylamines, with sodium chloroacetate.

Another preferred group of starting materials are glycinates or fattyacid amide-N, N-dialkyl betaines corresponding to formula (II): ##STR2##in which R⁴ CO is a saturated and/or unsaturated acyl radical containing6 to 22 carbon atoms, R⁵ is hydrogen or an alkyl and/or hydroxyalkylradical containing 1 to 4 carbon atoms, R⁶ is an alkyl and/orhydroxyalkyl radical containing 1 to 4 carbon atoms and n=2 or 3.Betaines corresponding to formula (II), in which R⁴ CO is an acylradical containing 8 to 18 carbon atoms, R⁵ and R⁶ represent a methyland/or hydroxyethyl group and n=3, are preferably used in the processaccording to the invention.

Thermal aftertreatment

A crucial precondition for the process according to the invention liesin the adjustment of the pH value. The pH value is normally adjusted byaddition of an alkali metal hydroxide to the water-containing pastes orsolutions of the betaines or amphoteric surfactants. The alkali metalhydroxides may be used in the form of 5 to 55% by weight aqueoussolutions and preferably in the form of 25 to 50% by weight aqueoussolutions. Concentrated sodium hydroxide solutions, i.e. approximately50% by weight sodium hydroxide solutions, are preferably used.

The alkalized betaines or amphoteric surfactants are then subjected to athermal aftertreatment. The aftertreatment may be carried out attemperatures of 20 to 130° C., for example in a stirred tank reactor. Inone preferred embodiment of the process according to the invention,however, the aftertreatment is carried out in a pressure vessel attemperatures of 90 to 120° C., optionally under an elevated autogenouspressure of around 1 to 2 bar. The primary object of the thermalaftertreatment is to reduce the content of dichloroacetic acid whichrequires a reaction time of 0.1 to 5 h and preferably 1 to 3 h. At thesame time, however, the content of any free monochloroacetic acidpresent is also significantly reduced, i.e. to below the instrumentdetection limit.

By contrast, if the objective is solely to achieve adequatestabilization against microbial contamination and to improve thebleachability of the surfactants, it is sufficient to adjust theproducts to a highly alkaline pH value at room temperature andimmediately to further treat them, for example to bleach them byaddition of 0.01 to 1% by weight and preferably 0.1 to 0.5% by weight ofhydrogen peroxide, based on the solids content of the products, attemperatures in the range from 50 to 95° C. and preferably attemperatures in the range from 60 to 90° C.

After the thermal treatment, the products may, if desired, be adjustedto a pH value in the range from 7 to 5, for example by addition ofmineral acid. If this measure is applied, the protection againstmicrobial contamination is of course lost.

Commercial Applications

The products obtainable by the process according to the invention havean extremely low residual content of dichloroacetic acid and arestabilized against microbial contamination without any need forpreservatives. Accordingly, they are suitable for the production ofsurface-active compositions, for example laundry detergents, dishwashingdetergents and cleaning products and also hair care and body careproducts, in which they may be present in quantities of 1 to 30% byweight and preferably 2 to 10% by weight, based on the particularproduct.

The following Examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES

I. Hydrolysis stability

C_(8/18) cocofatty acid amidopropyl-N,N-dimethylaminobetaine (Dehyton®K, a product of Henkel KGaA, Dusseldorf, FRG; solids content around 35%by weight) was adjusted to pH 11 by addition of aqueous sodium hydroxidesolution and stored for 8 weeks at 20° C. and 40° C. During time, the pHvalue and the acid and amine values monitored. The results are set outin Table 1 below:

                  TABLE 1    ______________________________________    Storage tests with Dehyton ® K               pH value       Acid value                                        Amine value    Ex. t      20° C.                       40° C.                              20° C.                                    40° C.                                          20° C.                                                40° C.    ______________________________________    1   0      11.00   11.00  3.0   3.0   0.50  0.50    2   1 d    10.89   11.31  2.7   3.1   0.47  0.53    3   3 d    10.74   11.24  2.7   3.1   0.50  0.50    4   5 d    10.66   11.24  2.6   2.9   0.50  0.50    5   2 w    10.46   10.96  2.9   2.9   0.47  0.47    6   3 w    10.42   10.92  2.9   2.8   0.47  0.50    7   4 w    10.20   10.90  2.9   2.8   0.50  0.47    8   8 w    10.20   10.88  2.9   3.0   0.50  0.53    ______________________________________     Legend: t = Storage time

The Examples show that, even under extreme storage conditions (pH 11,40° C., 8 weeks), the acid and amine values remain constant and nohydrolysis of the amide bond occurs.

II. Bleaching

0.1 to 1% by weight of hydrogen peroxide (30% by weight), based on thesolids content, was added to C_(8/18) cocofatty acidamidopropyl-N,N-dimethylaminobetaine (Dehyton® K, a product of HenkelKGaA, Dusseldorf, FRG; solids content approx. 35% by weight) atdifferent pH values, followed by bleaching for 30 minutes at 60° C. Theresults are set out in Table 2 below:

                  TABLE 2    ______________________________________    Bleaching of Dehyton ® K                        c(H.sub.2 O.sub.2)                                  Color value    Ex.   pH value      % by weight                                  APHA    ______________________________________    9     11            0.1       35    10    12            0.1       40    11    12            1.0       30    12    13            0.1       50    C1    7             --        100    C2    5             0.1       120    C3    3             0.1       125    C4    9             0.1       95    ______________________________________     Legend: c(H.sub.2 O.sub.2) = Concentration of bleaching agent

III. Dichloroacetic acid content

C_(8/18) cocofatty acid amidopropyl-N,N-dimethylaminobetaine (Dehyton®K, a product of Henkel KGaA, Dusseldorf, FRG; solids content around 35%by weight) was adjusted to pH 12.5 to 13.5 by addition of aqueous sodiumhydroxide solution (based on 10% by weight product solutions at 20° C.)and aftertreated in an autoclave for 0.5 to 3 h at a temperature of 90to 120° C. and under a pressure of 1 to 1.1 bar. The results relating tothe dichloroacetic acid content are set out in Table 3 below:

                  TABLE 3    ______________________________________    Dichloroacetic acid content in Dehyton ® K                    T        p   t     c(DCE)                                             c(Alk)    Ex.    pH value ° C.                             bar h     ppm   mmg    ______________________________________    C3     7.0                         97    90.7    C5     9.0      92       1.0 3.0   88    95.5    C6     10.5     92       1.0 3.0   86    98.4    13     13.0     92       1.0 0.5   68    129.3           13.0     92       1.0 1.0   61    129.3           13.0     92       1.0 2.0   49    129.3           13.0     92       1.0 3.0   38    129.3    14     13.5     92       1.0 0.5   62    132.9           13.5     92       1.0 1.0   60    132.9           13.5     92       1.0 2.0   46    132.9           13.5     92       1.0 3.0   34    132.9    15     13.5     120      1.1 1.0   5     136.4           13.5     120      1.1 2.0   5     136.4           13.5     120      1.1 3.0   2     136.4    16     12.5     120      1.1 1.0   25    114.3           12.5     120      1.1 2.0   5     114.3    ______________________________________     Legend:     T = Aftertreatment temperature     t = Aftertreatment time     p = Pressure     c(DCE) = content of dichloroacetic acid (via HPLC)     c(Alk) = Total alkali content after titration with perchloroacetic acid     mmg = mmoles/100 g

We claim:
 1. A process for reducing the content of dichloroacetic acid in a water-containing paste or solution of a betaine surfactant containing dichloroacetic acid residues wherein the betaine surfactant is at least one compound of the formula I or II ##STR3## in which R¹ is an alkyl or alkenyl radical containing from 6 to about 22 carbon atoms, and R² and R³ independently of one another represent an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, ##STR4## in which R⁴ CO is a saturated or unsaturated acyl radical containing 6 to 22 carbon atoms, R⁵ is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, R⁵ is an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, and n=2 or 3, comprising the steps ofA) adding an alkali metal hydroxide to said paste or solution until a pH in the range of from about 11 to about 14 is obtained; and B) thermally treating the resulting mixture until a significant reduction in residual dichloroacetic acid is achieved.
 2. The process of claim 1 wherein step B) is carried out at a temperature in the range of from about 20 to 130° C.
 3. The process of claim 2 wherein said temperature is in the range of from about 90 to about 120° C.
 4. The process of claim 2 wherein step B) is carried out for a period of from about 0.1 to about 5 hours.
 5. The process of claim 3 wherein step B) is carried out for a period of from about 1 to about 3 hours.
 6. The process of claim 1 wherein in step A) the pH is in the range of from about 12 to about 13.5.
 7. The process of claim 1 wherein step B) is carried out at a pressure of from 1 to about 2 bar.
 8. The process of claim 1 wherein the paste or solution in step A) contains at least one alkyl betaine of the formula: ##STR5## in which R¹ is an alkyl or alkenyl radical containing from 6 to about 22 carbon atoms, and R² and R³ independently of one another represent an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms.
 9. The process of claim 1 wherein the paste or solution in step A) contains at least one compound of the formula ##STR6## in which R⁴ CO is a saturated or unsaturated acyl radical containing 6 to 22 carbon atoms, R⁵ is hydrogen or an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, R⁵ is an alkyl or hydroxyalkyl radical containing 1 to 4 carbon atoms, and n=2 or
 3. 10. The process of claim 1 wherein in step A) the alkali metal hydroxide is sodium hydroxide.
 11. The process of claim 1 wherein the mixture resulting from step B) is then bleached with hydrogen peroxide.
 12. The process of claim 1 wherein the mixture resulting from step B) is adjusted to a pH in the range of from about 5 to about
 7. 13. The process of claim 1 wherein the pH is in the range of from about 12 to about 13.5; and step B) is carried out at a temperature in the range of from about 90 to about 120° C.
 14. The process of claim 13 wherein step B) is carried out for a period of from about 1 to about 3 hours under a pressure of from 1 to about 2 bar.
 15. In a laundry detergent, dishwashing detergent, or cleaning composition, the improvement wherein from about 1 to about 30% by weight of the product of the process of claim 1 is added thereto.
 16. The laundry detergent, dishwashing detergent, or cleaning composition of claim 15 wherein from about 2 to about 10% by weight of the product of the process of claim 1 is added thereto.
 17. A process for stabilizing against microbial contamination a water-containing paste or solution of a betaine or amphoteric surfactant free from dichloroacetic acid residues comprising adding an alkali metal hydroxide to said paste or solution until a pH in the range of from about 11 to about 14 is obtained.
 18. The process of claim 17 wherein said pH is in the range of from about 12 to about 13.5.
 19. The process of claim 17 wherein the alkali metal hydroxide is sodium hydroxide.
 20. The process of claim 17 wherein an additional step of bleaching with hydrogen peroxide is carried out on the paste or solution. 